Manufacture of rubber treated fiber



Patented May 8, 1945 Clark (3. Heritage, Cloquet, Minn., asslgnor toWood Conversion Company, Cloquet, Minn, a

corporation of Delaware No Drawing. Application May.22, 1940, Serial No.336,577

2 Claims.

suspension in water) by a high speed rotary disk or like means. Thepresent invention is directed to the use of rubber or like dispersionswith or without other agents, to treat the fibers as they are so formedby that process, and not after they are formed. t also relates to thesubsequent treatments of the so-treated fiber for uses for which thefiber is particularly adapted by such treatment.

One object of the invention is to introduce dispersed rubber or the liketo the grinding elements along with the raw material to be or beingdefibered.

A particular object of the invention is to add aqueous emulsions ofrubber or like material to wood or the like to be or being defibered ina gaseous atmosphere.

Another object 01' the invention is to dry the treated fiber so produceddirectly, whereby all the solid substances of ,the rubber dispersion andof the wood are preserved.

Still another object of the invention is to provide a highly usefulfiber for bulk insulation as mats, which are felted either with orwithout a binder, mechanically, pneumatically or other- Wise.

A particular object of the invention is to use a treating agent whichdoes not add an odor to the fiber.

Various other and ancillary objects and advantages of the invention willbecome apparent from the following description and explanation of theinvention.

Reference is first made to the U. S. Asplund Patents No. 2,145,851, No.2,008,892 and No.

. 2,047,170. relating respectively to a machine, the

process of said machine, and the use of a sir-e in such process andmachine. The said patents are more particularly directed to thepreparation of wood fiber for making fiber board. To these ends, thefiber is discharged from the machine, directly into water, and suchoperation masks a defect in the machine product which is troublesome insome uses 01' the fiber.

As set forth in the copending application Serial o. 227,338, filedAugust 29, 1938, of which the present application is a continuation inpart, the fiber need not be put into water, or wetted. For certain' usesit is dried directly from the moist condition which results fromdisintegration in a high pressure steam chamber. The moisture contentbased on the discharged moist fiber may vary from 40% to 60% andcommonly is about The drying is preferably done in ovens heated to about250 F. more or less, the temperature be- .ing not critical, but chosento effect drying for the conditions of loading the conveyor therethroughincluding its speed.

The directly-dried fiber is highly efficient as an insulating fiber tobe packed into spaces, particularly in refrigerators. So used, it iscustomary to bale the dry fiber, ship it to the point of use, break thebales and loosen the fiber, and then pack the fiber into its ultimateposition.

The fiber s0 handled from the drier, ls dusty to an undesirable degree.The dust is not only lost from the bulk, but it is a hazard to workmenand to machinery. As much as 5% of the original wood may be present asfiying dust, as a result of the necessary defibering action to attain afiber free from chips, slivers and like coarser bundles of fiber, all ofwhich lower the insulating efiiciency of the product.

When such fiber is pneumatically conveyed or packed, the presence ofdust is a disadvantage to this type of use. Such process may involvefilters, or filtration, and the dust may be too concentrated locally,giving poor thermal efilciency. Also, there are practical limitations inthe amount of force that may be used to felt fibers by a, pneumaticsystem. One effect of treatment according to the present invention is alowering of the resistance of the fiber to felting, whereby betterfelting for a given force is a desirable result.

The present invention shows that when rubber or rubber-like substance inhighly dispersed form, such as an aqueous latex emulsion, or a rubbersolution, is added to the raw material to be defibered, such as woodchips, 9. more useful product results. The amount of solid so added maybe controlled to vary many properties of the fiber as will later beshown. However, a small quantity may be added without greatly changingmany of those qualities which are considerably altered by largeramounts. Such smaller amount is quite efi'ective, however, to minimizethe dustiness of the product from the drier, and at other stages, and toalter the felting and other compressive properties. A specimen oflatex-treated fiber which has a given content of dustbefore baling,

' has a lessenedcontent of dust after being baled.

It appears that the act of compressing bonds loose dust or treated dustto the treated fibers to lessen fibers.

the dustiness. The terms dust, flying dust" and dustiness are hereinused to signify the same condition. The ,dust is considered to be thefine particles which are free to fioat in the air away from the masswhen it is in a loose flufiy condition, and is distinguished from thefibers or fines which are held in a felted aggregate from which the dustmay float away. The dust, may be broken fibers, particles, and evenultimate Not all the ultimate fiber content of a mass of fibers becomesflying dust. A mass of fibers serves as a matrix capable of retainingultimate fibers. From any matrix 'of fibers, that portion of it which iscapable-of leaving the matrix and of being carried off in the air, toappear as dust, is considered to be the dust content, or to indicate thedustiness. Obviously, it is not a clear cut fraction or component of themass, being dependent upon the size and density of the matrix, as wellas upon the characteristics of the matrix to hold or release the dust.The rubber treatment of the present invention affects thecharacteristics of the matrix so that it exhibits less dustiness. Afterbalin'g, the same fine particles may be present as before'baling, butthey are 'not free to fioat away, and are therefore 'not dust.

'Many methods may be develo'pedto determine dust content. The methodmust be some standard operation upon the fiber which gives reproducibleresults with specimens of the same batch, in order that the dustiness ofdifferent batches may be compared. One such method is described in thecopending application of Anway Serial No. 290,999, filed August 19,1939, now U. S. Patent 2,324,126, issued July 13, 1943.

As an example of the effect of a small amount of latex on fiber, thefollowing table shows jack pine fiber made in the Asplund machine underconditions to produce the same coarseness modulus (particle sizedistribution as determined by Wet screening the fibers to isolatefractions thereof). The differences in properties gi'ven below may notbe charged to difference in the composition of fiber, due to the sizesof the components, but may be charged to experimental errors indetermining them, and to the latex. Many experiments show that thedifference in dust content and improved felting qualities are due to thelatex.

Table 1 0.9% latex solids Numbers 3-202-46 and 47- Steam pressure,lbs/sq. in Compressive pro ertics:

Free footage in board feet per lb. 0.. Specific elasticity (at 315 boardfer-L per lb.) in lbs. per sq. ft Absolute elasticity Specific felting(at 3.15 board feet per 1b.) in lbs. per sq. it Absolute feltlug, anindex Coefficient of sliding friction, an index Thermal conductivity(ll. t. u./hr./s(1. fl../ "F, inch) Friability, uuindex Dust,pcrecntimpact resistance, board-feet pcr ll Fractionation, per cent content:

lstfraction I '1'. 2nd fraction... lits ll 3rd fraction 4th fractionPast 4th fraction. Coerscness modulus I 5 sun;

In the above table, the differences are due to the latex only, theSpecimens having been made under the same conditions of operation atsubstantially the same time. The properties designated compressiveproperties may be interpreted in terms of differences actually observedin using the fibers.

Oneuse of such fiber is inthe pneumatic process of packing them intorefrigerator spaces, as set forth in my application Serial No. 294,212,filed September 9, 1939. According'to such process fibers are introducedto a blower fan which forces them in air suspension through a conduitinto selected inlets to a space to be packed. Selected outlets areprovided, preferably with filters to release the air. In this processthere is an air force exerted on the fibers, and fibers are deposited infelted relation. The density of the felt increases with increase of airpressure, other conditions being the same. The propertydesignatedspecific felting means that at a density of 3.15 board feetper pound, the fiber with latex is less resistant to felting, or feltswith more ease at a given pressure applied to felt it than fiberwithoutlatex. Since increase of pressure in a pneumatic system is somewhatinvolved by economic and mechanical factors, the effect is obtained bytreating with latex to improve the fibers for a given mechanical outfit.The benefits from reduced dustare also highly desirable in operating thesame system. The compressive properties" may be determined as set forthin the application of Anway, Serial No. 313,920, filed January 15,

-Friability, dust and permanence to heat" These properties may bedetermined according to the process described in 'said An'way Patent No.2,324,126. This involves a standardized pounding of the fiber to createand measure dust formed. It incidentally gives by amathematicalintercept, an indication of original dust content. By heating fiber for24 hours at 150 C. and again measuring friability, a ratio offriabilities before and after heating, is found as a measure ofpermanence to heat.

Friability" is expressed as a mathematical term which is the slope ofthe straight line obtained by plotting horizontally, the minutes" ofpounding time, and vertically, the ratio of fiber loss of originalspecimen to remnant of the original specimen.

The free-footage is determined as one of the "compressive properties,"and is an extrapolated value defined as the natural density of thefiber-at zero compression. The. table shows that the treated fiber isnaturally less-bulky.

In giving references to other applica 'ons for letters patent herein, itis to be understood that these are not given as essential to the presentdisclosure, or for amplifying it, but; only v for the purposeofassociating the several inventions into arelated group.

In the foregoing Table 1. the 9%" solids from the rubber latex reducethe original d'ustiness from In said patent under the sub-title- 2.8% to1.0%. After baling the 1% of dust is reduced materially, depending uponbaling pressure. Smaller percentages of latex give results to aproportionate degree,and the preferred content is from .9% to 1%.Additional quantities. are not proportionately effective to reduce thedust, but they alter the various properties of the fiber above listed.Hence, where it is desired so to change these properties, more latex maybe added.

Each substance used to treat fibers has its specific effect upondifferent properties, which effects may be determined only by thetedious. task of actually running the defibrator machine with a seriesof treatments by each material indifferent quantities, and thentediously determining the various properties. This has been done withlatex, and other materials, of which A and B are indicated, merely forthe purpose of showing. the specificity of materials. Under thesubtitles of the property measured, given below, are given specificefiects'of increased contents of latex, of A, and of B. However. theseelfects'must not be considered as absolute to the degree that they maybe compared with the data in Table 1, for the reasons given in the nextparagraph.

In Table 1 it is to be noted particularly that the fiber masses comparedhave the same coarseness modulus so that the differences in theproperties cannot be attributed to differences in particl -sizedistribution. A change in the coarseness modulus also effects propertiesenumerated in Table 1. It has also been determined that with the samecoarseness modulus, the actual distribution of sizes may change. It hasalso been determined that two different sizes of defibrator machinesyielding fibers having the sam coarseness modulus will give fibershavingdifferent properties, for example different dustiness. The manner inwhich treating agents affect the properties of the fiber are not alwaysthe same in different sizes of machines. The materials A and B, abovereferred to and latex have been compared by using a machine of sizedifferent from the size used for the fibers of Table 1. Also the fibersproduced in the following comparisons have not a constant coarsenessmodulus and lie generally in the range from 225 to 250. Therefore, someof the effects, and apparent discrepancies may be due in part to avariation in particle size. However, sufficient variations are evidentto show that the materials A and B, and latex, act specifically. Suchshowing is the purpose of the following comparisons.

Coefii cient of sliding friction Increase of l atex markedly decreasesthe property. For example one series showed it to vary one seriesreduced it from 118. to 85 by a usage from 4% to being not veryeffective below Absolute elasticity Free footage Use of latex tends toreduce this property.

Material A drops the free-footage. One series showed a drop from 7.2 to4.7 in usage from zero to Material B also drops the free footage. Forexample, one series showed it to drop from 8 to 7.4 in a usage up to15%.

In the same way other properties may be compared with thematerials:latex, material A, and

. material B, said materials A and B, being the subject matter for otherapplications for letters patent, inasmuch as they are of differentnature and each has its specific effects.

Modifying ingredients Agents to vulcanize the rubber solids may be addedwithout indication of any great change in the dust-reducing function.Accelerators, anti-oxidant compounds, and other materials commonly usedin association with rubber are contemplated herein as modifying agents.These may be present in the dispersion with the rubber, or addedseparately.

Fire-proofing agents Preservatives Agents to prevent decay, mould andinsect attack may be added with the latex. For exfrom .884 to 5712 by anincrease up to 10% solids of latex.

Material A increases the property. Specifi cally, a series showed it tochange from 1.09 to 2.57 when used up to 40% of A.

Material B increases the property. Specifically, one series showed it toincrease from .852 to 1.40 up to 8%, and then to decrease againthereafter.

Specific elasticity Latex increases the property. Specifically, one

series showed it to increase from 153 to 182 by increase of latex solidsto 8%.

Material A lowers the property. one series showed it to be lowered from267 to 19.5 by usage of A up to 40%.

Material B lowers the property. Specifically,

Specifically interior.

ample, tetrachlorphenol and pentachlorphenol or their sodium salts maybe used, as described in Serial No. 345,610, filed July 15, 1940.Alkalis may also be used without destroying the func- V tions of thelatex.

Pneumatic felting moisture from the insulation. For this reason I thereare vents from the fiber to the refrigerator Use of any fiber carryingan odorous treating agent in such a vented box, will odorize the food inthe refrigerator. Thus, some rubber emulsions will give a so-calledrubber odor, but latex is one which is free from odor. This is also trueof the fiber made from non-vulcanizing rubber cement solutions.

Where odor is not a requirement to be considered, dispersions,preferably as water-emul sions of rubber or rubber derivatives may beused, and are to. be considered within the broad scope of the inventionunder the term ,rubber dispersion." Solutions of rubber or'the like inorganic volatile solvents are useful, but; owing to the loss of volatilesolvent in'process, the aqueous emulsions are the preferred dispersions.Where fiber is dried in an oven at high temperature solvent vaporscreate a fire-hazard. Hence aqueous dispersions are preferred. By theterm rubber,/ it is intended to comprehend rubber latex, rubberlikeproducts derived from natural rubber, the synthetic rubbers, and otherbalata-like substances.

In practice, the emulsion is employed as the preferred means initiallyto produce a fine dispersion of the rubber. What happens to the emulsionin the machine isnot known, except that the solid content is distributedonto the fiber discharged. The emulsion may be mixed with wood chipsentering the pressure chamber of the Asplund machine. The wood is out ofthe machine as fiber in about 60 seconds more or less after it entersthe pressure chamber. The entry of wood into the machine is rapidlyintermittent, and for all practical purposes it may beconsidered asbeing fed to the machine at a constant rate. The emulsion is also fed ata constant rate in the proportion desired for the treatment. Theemulsion may enter with the feed, or it may be injected into thepressure chamber or directly to the grinding means independently of thefeed of wood or other vegetable matter, and in the chamber bedistributed onto the wood by the grinding means. Byinjecting it into thechamber it mixes with the wood or the like before the latter contactsthe defibering means. By. injecting it to the grinding elements, itcontacts the vegetable matter prior to completion of the defiberingaction.

Latex emulsions are obtainable commercially in high concentrations offrom 40% to 60% solids. In practice, to insure greater dispersion of lowusages of the rubber, the solid are kept below 50%, such as at 40% or30%. In diluting concentrated commercial latex emulsions, it isdesirable to add an alkaline stabilizer. Thus in diluting 100 lbs. oflatex emulsions having 60% solids, to one of 40% solids 2 lbs. of 26ammonia (concentrated) solution is added. The water introduced is slightin comparison to the water which may I enter with the wood, but wherelarge amounts of .latex are employed a control of water in the wood maybeefiected if compensation is desired. Such compensation may beimportant.

Where the fiber is desirably dried directly from the machine, ratherthan being taken up in water, a lowered watercontent makes thedischarged fiber more fluffy or bulky, and hence easier and less costlyto dry, giving a more useful insulating fiber. For example where jackpine wood with 131% moisture (based on dry weight of wood), is used witha 40% latex emulsion, 2 parts by weight of the emulsion is used to 100parts by weight of dry wood.

The fiber is dried directly toan insulating fiber. Theconditionof thewood is also a considerable factor. To get the same dust-reducingbenefit with oldjack pine as with green jack pine, more latex isrequired. But the old wood dries so much easier that the oven may bekept at 49 F. lower. Thus, basing percentages on dry wood content, acomparison shows:

Table 2 Year old Green jack jack pine pine Per cent latex (40% solids)3. 63 2. Per cent dust 2 2. l. Dryer temperature. 203 252 Per cent chipmoisture 5 102.9 Per cent water added with wood 5 Table 3 illustratesthe invention comparing a control or untreated fiber, with othersproduced under the same conditions, one using rubber latex, and anotherusing rubber cement solution. Rough green jack pine wood is run throughthe 'Asplund defibrator set and operated without change to produce fiberfrom chips of the wood. The discharged fiber is designated 8-131-107.Then 30% latex is added tothe chips to add .75% rubber solids based ondry wood weight. The discharged fiber is designated S-131-106. Then thelatex is changed is add an 8% rubber cement solution in benzol, to add375% rubber solids based on dry weight of wood. The fiber is designatedS131-105. This fiber is dried, and evaluated as to particle sizedistribution, impact resistance, compressive properties, dust content,friability and permanence to heat, as recorded in Table 3.

Table 3 [Rough jack pine wood chips] Item Untreated Latex Cement Sample3-131 1U! 106 105 (Join ressive properties:

ree footage 9. 57 9. 52 9. 75

Specific elasticity (K a) 160 117 135 Absolute clasticlltz' (M x 343 3323 Specific felting r) 20. 2 3i. 2 38. 5

Absolute felting (M l") 249 234 241' Coefficient sliding friction l 1 lCoarseness modulus. 172 198 205 Impact resistance 3. 82 3. 3. 73 1Acidity (pH)..- 4. 05 4. 2o 4. so Friability U093 U052 002B Permanenceto heat 366 .258 162i .lercent dust (by screening) 3. 9 1. 9 2. 4

- vention isclaimed as practically limited, and also as a processindependent of the Asplund machine.

I claim:

. 1. The method of making dry vegetable fibers suitable for; formingloosely felted fiber mats, which comprises subjecting vegetable matterto be reduced to fiber to -the defibering action of mechanicaldefibering and mixing means in a gaseous atmosphere, and in the presenceof a non-suspending and a fiber-moistening amount of water, introducingdispersed rubber to the vegetable matter prior to completion of thedefibering and distributing said rubber into the loosening the compactedfibers the loosened fibers are less dusty than the fibers prior to saidcompacting.

2. The method of making dry wood fibers suitable for forming looselyfelted lignocellulose fiber mats, which comprises subjecting wood to bereduced to fiber to the action of a high-speed rotary element having adefibering and mixing action, in an atmosphere of steam at a temperaturePatent No. 2,575,1nh.

elevated above 212' F. and at which lignin in the lignocellulose becomessoftened to permit easy defibration, and in the'abs'ence of a suspendingamount of water, introducing dispersed rubber to said material prior tocompletion of defibration and distributing said rubber into the fibermass as the fiber is being finally formed, whereby moist rubber-sizedfibers are formed including a quantity of dust-forming particlesincidentally formed with said fibers, drying said moist rubher-sizedfibers to remove moisture and provide dry fibers, said rubber serving tobind some dustiorming particles to fibers to limit the dustiness of saiddry fibers, and compacting the dry fibers whereby residual free dustparticles are caused to adhere to the rubber-sized fibers, whereby uponloosening the compacted fibers the loosened fibers are less dusty thanthe fibers prior to said compacting.

CLARK C. HERITAGE.

CERI'IF ICATE OF CORREC 'II ON.

i b y 8, 9 5- GLARK C, HERITAGE.

It s r y l' that error appears in the printed-specification of the abovenumbered patent requiring correction as follows: Page 2, second column,line 69, after "herein" .and before the comma insert the Words -orpatents --affects--- page first column, line 51, for "effects" line 57,after the syllable "arty" and before the period inread 7 sort designatedcoefficient' of sliding friction, whi h is one of the com- I Pressive Pp line 69, after "pr p y" and before the 'period insert "designatedspecific elasticity, which is one of the compressive properties--;

and second column, line 5, after "property" and before the comma insert"designated absolute elasticity, which is one of the compressivepropertiesinsert the following paragraph,

, page 14., second column, line '65, before "I claim:''

"The present application is a 'continuation-in-part of my priorapplication, Serial No. 227,358, filed August 29, 19 and abandoned.August as, 19L 2.-

and that the said Letters Patent should be read with this correctiontherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 25th day of September, A. v

(Seal) Leslie Frazer First Assistant Commissioner of Patents.

loosening the compacted fibers the loosened fibers are less dusty thanthe fibers prior to said compacting.

2. The method of making dry wood fibers suitable for forming looselyfelted lignocellulose fiber mats, which comprises subjecting wood to bereduced to fiber to the action of a high-speed rotary element having adefibering and mixing action, in an atmosphere of steam at a temperaturePatent No. 2,575,1nh.

elevated above 212' F. and at which lignin in the lignocellulose becomessoftened to permit easy defibration, and in the'abs'ence of a suspendingamount of water, introducing dispersed rubber to said material prior tocompletion of defibration and distributing said rubber into the fibermass as the fiber is being finally formed, whereby moist rubber-sizedfibers are formed including a quantity of dust-forming particlesincidentally formed with said fibers, drying said moist rubher-sizedfibers to remove moisture and provide dry fibers, said rubber serving tobind some dustiorming particles to fibers to limit the dustiness of saiddry fibers, and compacting the dry fibers whereby residual free dustparticles are caused to adhere to the rubber-sized fibers, whereby uponloosening the compacted fibers the loosened fibers are less dusty thanthe fibers prior to said compacting.

CLARK C. HERITAGE.

CERI'IF ICATE OF CORREC 'II ON.

i b y 8, 9 5- GLARK C, HERITAGE.

It s r y l' that error appears in the printed-specification of the abovenumbered patent requiring correction as follows: Page 2, second column,line 69, after "herein" .and before the comma insert the Words -orpatents --affects--- page first column, line 51, for "effects" line 57,after the syllable "arty" and before the period inread 7 sort designatedcoefficient' of sliding friction, whi h is one of the com- I Pressive Pp line 69, after "pr p y" and before the 'period insert "designatedspecific elasticity, which is one of the compressive properties--;

and second column, line 5, after "property" and before the comma insert"designated absolute elasticity, which is one of the compressivepropertiesinsert the following paragraph,

, page 14., second column, line '65, before "I claim:''

"The present application is a 'continuation-in-part of my priorapplication, Serial No. 227,358, filed August 29, 19 and abandoned.August as, 19L 2.-

and that the said Letters Patent should be read with this correctiontherein that the same may conform to the record of the case in thePatent Office.

Signed and sealed this 25th day of September, A.

(Seal) Leslie Frazer First Assistant Commissioner of Patents.

